How to invite existing Fisheye/SVN OnDemand users into BitBucket

Now that we have chosen to go with BitBucket, linked it with our existing OnDemand package, and created the admin account, we are looking to add all our existing users to the developers group. We have around 100 users, but we don't seem to find them easily in the BitBucket admin screens.

Are we doing something wrong?

Do we have to invite each one of these users individually? I hope not!